Implement mdmcert.download support in mdmctl (#401)

Gopkg.lock

@@ -21,7 +21,7 @@
   branch = "master"
   name = "github.com/fullsailor/pkcs7"
   packages = ["."]
-  revision = "a009d8d7de53d9503c797cb8ec66fa3b21eed209"
+  revision = "ae226422660e5ca10db350d33f81c6608f3fbcdd"
 
 [[projects]]
   branch = "master"

cmd/mdmctl/mdmcert.download.go

@@ -0,0 +1,284 @@
+package main
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"encoding/pem"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+
+	"github.com/fullsailor/pkcs7"
+	"github.com/go-kit/kit/log"
+	"github.com/micromdm/micromdm/pkg/crypto"
+	"github.com/micromdm/micromdm/pkg/crypto/mdmcertutil"
+	"github.com/pkg/errors"
+)
+
+const (
+	mdmcertRequestURL = "https://mdmcert.download/api/v1/signrequest"
+	// see
+	// https://github.com/jessepeterson/commandment/blob/1352b51ba6697260d1111eccc3a5a0b5b9af60d0/commandment/mdmcert.py#L23-L28
+	mdmcertAPIKey = "f847aea2ba06b41264d587b229e2712c89b1490a1208b7ff1aafab5bb40d47bc"
+)
+
+// format of a signing request to mdmcert.download
+type signRequest struct {
+	CSR     string `json:"csr"` // base64 encoded PEM CSR
+	Email   string `json:"email"`
+	Key     string `json:"key"`     // server key from above
+	Encrypt string `json:"encrypt"` // mdmcert pki cert
+}
+
+type mdmcertDownloadCommand struct {
+	*remoteServices
+}
+
+func (cmd *mdmcertDownloadCommand) setup() error {
+	logger := log.NewLogfmtLogger(os.Stderr)
+	remote, err := setupClient(logger)
+	if err != nil {
+		return err
+	}
+	cmd.remoteServices = remote
+	return nil
+}
+
+func (cmd *mdmcertDownloadCommand) Usage() error {
+	const usageText = `
+Request new MDM Push Certificate from https://mdmcert.download
+This utility helps obtain an MDM Push Certificate using the service
+at mdmcert.download.
+
+First we'll generate the initial request (which also generates a private key):
+
+	mdmctl mdmcert.download -new -email=cool.mdm.admin@example.org
+
+This will output the private key into the file mdmcert.download.key.
+Then, after you check your email and download the request file you just
+need to decrypt the push certificate request:
+
+	mdmctl mdmcert.download -decrypt=~/Downloads/mdm_signed_request.20171122_094910_220.plist.b64.p7
+
+This will output the push certificate request to mdmcert.download.req.
+Upload this file to https://identity.apple.com and download the signed
+certificate. Then use the 'mdmctl mdmcert upload' command to upload it,
+(and the above private key) into MicroMDM.
+
+`
+	fmt.Println(usageText)
+	return nil
+
+}
+
+func (cmd *mdmcertDownloadCommand) Run(args []string) error {
+	flagset := flag.NewFlagSet("mdmcert.download", flag.ExitOnError)
+	flagset.Usage = usageFor(flagset, "mdmctl mdmcert.download [flags]")
+	var (
+		flNew       = flagset.Bool("new", false, "Generates a new privkey and uploads new MDM request")
+		flDecrypt   = flagset.String("decrypt", "", "Decrypts and mdmcert.download push certificate request")
+		flEmail     = flagset.String("email", "", "Email address to use in mdmcert request & CSR Subject")
+		flCountry   = flagset.String("country", "US", "Two letter country code for the CSR Subject (example: US).")
+		flCN        = flagset.String("cn", "mdm-push", "CommonName for the CSR Subject.")
+		flCertPath  = flagset.String("pki-cert", "mdmcert.download.pki.crt", "Path for generated MDMCert pki exchange certificate")
+		flKeyPath   = flagset.String("pki-private-key", "mdmcert.download.pki.key", "Path for generated MDMCert pki exchange private key")
+		flPKeyPass  = flagset.String("pki-password", "", "Password to encrypt/read the RSA key.")
+		flCCSRPath  = flagset.String("push-csr", "mdmcert.download.push.csr", "Path for generated Push Certificate CSR")
+		flCReqPath  = flagset.String("push-req", "mdmcert.download.push.req", "Path for generated Push Certificate Request")
+		flCKeyPath  = flagset.String("push-private-key", "mdmcert.download.push.key", "Path to the generated Push Cert private key")
+		flCPKeyPass = flagset.String("push-password", "", "Password to encrypt/read the push RSA key.")
+	)
+
+	if err := flagset.Parse(args); err != nil {
+		cmd.Usage()
+		return err
+	}
+
+	// neither flag was used
+	if !*flNew && *flDecrypt == "" {
+		cmd.Usage()
+		return errors.New("bad input: must either use -new or -decrypt")
+	}
+
+	// both flags used
+	if *flNew && (*flDecrypt != "") {
+		// cmd.Usage()
+		return errors.New("bad input: can't use both -new and -decrypt")
+	}
+
+	if *flNew {
+		if *flEmail == "" {
+			return errors.New("bad input: must provide -email")
+		}
+
+		paths := []string{*flCertPath, *flKeyPath, *flCCSRPath, *flCKeyPath}
+		for _, path := range paths {
+			if _, err := os.Stat(path); err == nil {
+				return fmt.Errorf("file already exists: %s", path)
+			}
+		}
+
+		pkiKey, pkiCert, err := crypto.SimpleSelfSignedRSAKeypair("mdmcert.download", 365)
+		if err != nil {
+			return errors.Wrap(err, "could not create PKI keypair")
+		}
+
+		pemBlock := &pem.Block{
+			Type:    "CERTIFICATE",
+			Headers: nil,
+			Bytes:   pkiCert.Raw,
+		}
+		pemPkiCert := pem.EncodeToMemory(pemBlock)
+
+		if err := crypto.WritePEMCertificateFile(pkiCert, *flCertPath); err != nil {
+			return errors.Wrap(err, "could not write PKI cert")
+		}
+
+		if *flPKeyPass != "" {
+			err = crypto.WriteEncryptedPEMRSAKeyFile(pkiKey, []byte(*flPKeyPass), *flKeyPath)
+		} else {
+			err = crypto.WritePEMRSAKeyFile(pkiKey, *flKeyPath)
+		}
+		if err != nil {
+			return errors.Wrap(err, "could not write private key")
+		}
+
+		pushKey, err := rsa.GenerateKey(rand.Reader, 2048)
+		if err != nil {
+			return errors.Wrap(err, "could not generate push private key")
+		}
+
+		if *flCPKeyPass != "" {
+			err = crypto.WriteEncryptedPEMRSAKeyFile(pushKey, []byte(*flCPKeyPass), *flCKeyPath)
+		} else {
+			err = crypto.WritePEMRSAKeyFile(pushKey, *flCKeyPath)
+		}
+		if err != nil {
+			return errors.Wrap(err, "could not write push private key")
+		}
+
+		derBytes, err := mdmcertutil.NewCSR(pushKey, *flEmail, *flCountry, *flCN)
+		if err != nil {
+			return errors.Wrap(err, "could not generate push CSR")
+		}
+		pemCSR := mdmcertutil.PemCSR(derBytes)
+		// Do we even need to write-out the CSR?
+		err = ioutil.WriteFile(*flCCSRPath, pemCSR, 0600)
+		if err != nil {
+			return errors.Wrap(err, "could not write PEM file")
+		}
+
+		sign := newMdmcertDownloadSignRequest(*flEmail, pemCSR, pemPkiCert)
+		req, err := sign.HTTPRequest()
+		if err != nil {
+			return errors.Wrap(err, "could not create http request")
+		}
+		err = sendMdmcertDownloadRequest(http.DefaultClient, req)
+		if err != nil {
+			return errors.Wrap(err, "error sending http request")
+		}
+
+		fmt.Print("Request successfully sent to mdmcert.download. Your CSR should now\n" +
+			"be signed. Check your email for next steps. Then use the -decrypt option\n" +
+			"to extract the CSR request which will then be uploaded to Apple.\n")
+
+	} else { // -decrypt switch
+		if _, err := os.Stat(*flCReqPath); err == nil {
+			return fmt.Errorf("file already exists: %s", *flCReqPath)
+		}
+		hexBytes, err := ioutil.ReadFile(*flDecrypt)
+		if err != nil {
+			return errors.Wrap(err, "reading encrypted file")
+		}
+		pkcsBytes, err := hex.DecodeString(string(hexBytes))
+		if err != nil {
+			return errors.Wrap(err, "error decoding hex")
+		}
+		pkiCert, err := crypto.ReadPEMCertificateFile(*flCertPath)
+		if err != nil {
+			return errors.Wrap(err, "reading PKI certificate")
+		}
+		var pkiKey *rsa.PrivateKey
+		if *flPKeyPass != "" {
+			pkiKey, err = crypto.ReadEncryptedPEMRSAKeyFile(*flKeyPath, []byte(*flPKeyPass))
+		} else {
+			pkiKey, err = crypto.ReadPEMRSAKeyFile(*flKeyPath)
+		}
+		if err != nil {
+			return errors.Wrap(err, "reading PKI private key")
+		}
+		ioutil.WriteFile("/tmp/fubar.p7", pkcsBytes, 0666)
+		p7, err := pkcs7.Parse(pkcsBytes)
+		if err != nil {
+			return errors.Wrap(err, "parsing mdmcert PKCS7 response")
+		}
+		// fmt.Println(p7)
+		content, err := p7.Decrypt(pkiCert, pkiKey)
+		if err != nil {
+			return errors.Wrap(err, "decrypting mdmcert PKCS7 response")
+		}
+		err = ioutil.WriteFile(*flCReqPath, content, 0666)
+		if err != nil {
+			return errors.Wrap(err, "writing Push Request response")
+		}
+
+		fmt.Printf("Successfully able to decrypt the MDM Push Certificate request! Please upload\n"+
+			"the file '%s' to Apple by visiting https://identity.apple.com\n"+
+			"Once your Push Certificate is signed by Apple you can download it\n"+
+			"and import it into MicroMDM using the `mdmctl mdmcert upload` command\n", *flCReqPath)
+	}
+
+	return nil
+}
+
+func newMdmcertDownloadSignRequest(email string, pemCSR []byte, serverCertificate []byte) *signRequest {
+	encodedCSR := base64.StdEncoding.EncodeToString(pemCSR)
+	encodedServerCert := base64.StdEncoding.EncodeToString(serverCertificate)
+	return &signRequest{
+		CSR:     encodedCSR,
+		Email:   email,
+		Key:     mdmcertAPIKey,
+		Encrypt: encodedServerCert,
+	}
+}
+
+func (sign *signRequest) HTTPRequest() (*http.Request, error) {
+	buf := new(bytes.Buffer)
+	if err := json.NewEncoder(buf).Encode(sign); err != nil {
+		return nil, err
+	}
+	req, err := http.NewRequest("POST", mdmcertRequestURL, ioutil.NopCloser(buf))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add("User-Agent", "micromdm/certhelper")
+	return req, nil
+}
+
+func sendMdmcertDownloadRequest(client *http.Client, req *http.Request) error {
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("received bad status from mdmcert.download. status=%q", resp.Status)
+	}
+	var jsn = struct {
+		Result string
+	}{}
+	if err := json.NewDecoder(resp.Body).Decode(&jsn); err != nil {
+		return err
+	}
+	if jsn.Result != "success" {
+		return fmt.Errorf("got unexpected result body: %q\n", jsn.Result)
+	}
+	return nil
+}

cmd/mdmctl/mdmdctl.go

@@ -38,6 +38,9 @@ func main() {
 	case "mdmcert":
 		cmd := new(mdmcertCommand)
 		run = cmd.Run
+	case "mdmcert.download":
+		cmd := new(mdmcertDownloadCommand)
+		run = cmd.Run
 	default:
 		usage()
 		os.Exit(1)
@@ -58,6 +61,7 @@ Available Commands:
 	config
 	remove
 	mdmcert
+	mdmcert.download
 	version
 
 Use micromdm <command> -h for additional usage of each command.

pkg/crypto/helpers.go

@@ -8,11 +8,12 @@ import (
 	"encoding/asn1"
 	"encoding/pem"
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"math/big"
 	"os"
-	"time"
 	"strings"
+	"time"
 )
 
 func GenerateRandomCertificateSerialNumber() (*big.Int, error) {
@@ -66,6 +67,11 @@ func ReadPEMCertificateFile(path string) (*x509.Certificate, error) {
 	return certs[0], nil
 }
 
+const (
+	rsaPrivateKeyPEMBlockType = "RSA PRIVATE KEY"
+	certificatePEMBlockType   = "CERTIFICATE"
+)
+
 func ReadPEMCertificatesFile(path string) ([]*x509.Certificate, error) {
 	pemData, err := ioutil.ReadFile(path)
 	if err != nil {
@@ -76,7 +82,7 @@ func ReadPEMCertificatesFile(path string) ([]*x509.Certificate, error) {
 	for {
 		var block *pem.Block
 		block, rest = pem.Decode(rest)
-		if block == nil || block.Type != "CERTIFICATE" {
+		if block == nil || block.Type != certificatePEMBlockType {
 			return nil, errors.New("failed to decode PEM block containing certificate")
 		}
 		asn1data = append(asn1data, block.Bytes...)
@@ -87,6 +93,40 @@ func ReadPEMCertificatesFile(path string) ([]*x509.Certificate, error) {
 	return x509.ParseCertificates(asn1data)
 }
 
+func ReadPEMRSAKeyFile(path string) (*rsa.PrivateKey, error) {
+	return ReadEncryptedPEMRSAKeyFile(path, nil)
+}
+
+func ReadEncryptedPEMRSAKeyFile(path string, password []byte) (*rsa.PrivateKey, error) {
+	pemData, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	pemBlock, _ := pem.Decode(pemData)
+	if pemBlock == nil {
+		return nil, errors.New("PEM decode failed")
+	}
+	if pemBlock.Type != rsaPrivateKeyPEMBlockType {
+		return nil, fmt.Errorf("expecting PEM type of %s, but got %s", rsaPrivateKeyPEMBlockType, pemBlock.Type)
+	}
+
+	if x509.IsEncryptedPEMBlock(pemBlock) {
+		if password == nil {
+			return nil, errors.New("no supplied password for encrypted PEM")
+		}
+		derBytes, err := x509.DecryptPEMBlock(pemBlock, password)
+		if err != nil {
+			return nil, err
+		}
+		return x509.ParsePKCS1PrivateKey(derBytes)
+	} else if password != nil {
+		return nil, errors.New("supplied PEM password, but not encrypted")
+	}
+
+	return x509.ParsePKCS1PrivateKey(pemBlock.Bytes)
+}
+
 func WritePEMCertificateFile(cert *x509.Certificate, path string) error {
 	file, err := os.Create(path)
 	if err != nil {
@@ -97,7 +137,7 @@ func WritePEMCertificateFile(cert *x509.Certificate, path string) error {
 	return pem.Encode(
 		file,
 		&pem.Block{
-			Type:  "CERTIFICATE",
+			Type:  certificatePEMBlockType,
 			Bytes: cert.Raw,
 		})
 }
@@ -112,11 +152,31 @@ func WritePEMRSAKeyFile(key *rsa.PrivateKey, path string) error {
 	return pem.Encode(
 		file,
 		&pem.Block{
-			Type:  "RSA PRIVATE KEY",
+			Type:  rsaPrivateKeyPEMBlockType,
 			Bytes: x509.MarshalPKCS1PrivateKey(key),
 		})
 }
 
+func WriteEncryptedPEMRSAKeyFile(key *rsa.PrivateKey, password []byte, path string) error {
+	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0700)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	encPemBlock, err := x509.EncryptPEMBlock(
+		rand.Reader,
+		rsaPrivateKeyPEMBlockType,
+		x509.MarshalPKCS1PrivateKey(key),
+		password,
+		x509.PEMCipher3DES)
+	if err != nil {
+		return err
+	}
+
+	return pem.Encode(file, encPemBlock)
+}
+
 // TopicFromCert extracts the push certificate topic from the provided certificate.
 func TopicFromCert(cert *x509.Certificate) (string, error) {
 	var oidASN1UserID = asn1.ObjectIdentifier{0, 9, 2342, 19200300, 100, 1, 1}

pkg/crypto/mdmcertutil/certutil.go

@@ -43,11 +43,11 @@ func CreateCSR(req *CSRConfig) error {
 		return err
 	}
 
-	derBytes, err := newCSR(key, strings.ToLower(req.Email), strings.ToUpper(req.Country), req.CommonName)
+	derBytes, err := NewCSR(key, strings.ToLower(req.Email), strings.ToUpper(req.Country), req.CommonName)
 	if err != nil {
 		return err
 	}
-	pemCSR := pemCSR(derBytes)
+	pemCSR := PemCSR(derBytes)
 	return ioutil.WriteFile(req.CSRPath, pemCSR, 0600)
 }
 
@@ -145,7 +145,7 @@ const (
 )
 
 // create a CSR using the same parameters as Keychain Access would produce
-func newCSR(priv *rsa.PrivateKey, email, country, cname string) ([]byte, error) {
+func NewCSR(priv *rsa.PrivateKey, email, country, cname string) ([]byte, error) {
 	subj := pkix.Name{
 		Country:    []string{country},
 		CommonName: cname,
@@ -161,7 +161,7 @@ func newCSR(priv *rsa.PrivateKey, email, country, cname string) ([]byte, error)
 }
 
 // convert DER to PEM format
-func pemCSR(derBytes []byte) []byte {
+func PemCSR(derBytes []byte) []byte {
 	pemBlock := &pem.Block{
 		Type:    csrPEMBlockType,
 		Headers: nil,